• # question_answer A bullet of mass $20\,\,g$ is fired from a rifle of $8\,\,kg$ with an initial velocity of$100\,\,m\,\,{{s}^{-1}}$. Find the final velocity of the recoil of the rifle. A) $-0.25\,\,m\,\,{{s}^{-1}}$                     B) $2.5\,\,m\,\,{{s}^{-1}}$ C) $25\,\,m\,\,{{s}^{-1}}$            D)        $250\,\,m\,\,{{s}^{-1}}$

Initial momentum$=0$ Final momentum$=(0.02\times 100)+8\times v$ According to the law of conservation of momentum, $(0.02\times 100)+8v=0$,          $8v=-2$ $v=-\frac{1}{4}m{{s}^{-1}}=-0.25\,\,m\,\,{{s}^{-1}}$